反序列化时,C#类中的字段初始化程序不运行

Question

我有一个定义受保护字段的类.受保护的字段具有字段初始值设定项.

当我反序列化具体类时,不会运行字段初始值设定项.为什么？解决问题的最佳模式是什么？如果我将初始化移动到构造函数中,也不会调用构造函数.

[DataContract]
public class MyConcrete
{
    // FIELD INITIALIZER DOES NOT RUN WHEN COMMENTED IN:
    protected readonly Dictionary<int, string> myDict;// = new Dictionary<int, string>();

    public MyConcrete()
    {
        myDict = new Dictionary<int, string>();
    }

    private bool MyMethod(int key)
    {
        return myDict.ContainsKey(key);
    }

    private int myProp;

    [DataMember]
    public int MyProp
    {
        get { return myProp; }
        set { bool b = MyMethod(value); myProp = value; } // Call MyMethod to provoke error
    }
}

原始类层次结构

[DataContract]
public abstract class MyAbstract
{
    // THIS INITIALIZER IS NOT RUN WHILE DESERIALIZING:
    protected readonly Dictionary<int, string> myDict = new Dictionary<int, string>();

    private bool MyMethod(int key)
    {
        return myDict.ContainsKey(key);
    }

    private int myProp;

    [DataMember]
    public int MyProp
    {
        get { return myProp; }
        set { bool b = MyMethod(value); myProp = value; } // Call MyMethod to provoke error
    }
}

[DataContract]
public class MyConcrete : MyAbstract
{

}

class Program
{
    static void Main(string[] args)
    {
        string tempfn = Path.GetTempFileName();

        MyConcrete concrete = new MyConcrete() { MyProp = 42 };
        string data = concrete.SerializeToString<MyConcrete>();

        MyConcrete rehydrated = SerializationHelper.DeserializeFromString<MyConcrete>(data);
    }
}

支持方法

static public string SerializeToString<T>(this T obj)
{
    return SerializationHelper.SerializeToString<T>(obj);
}

static public string SerializeToString<T>(T obj)
{
    DataContractSerializer s = new DataContractSerializer(typeof(T));
    using (MemoryStream ms = new MemoryStream())
    {
        s.WriteObject(ms, obj);
        ms.Position = 0;
        using (StreamReader sr = new StreamReader(ms))
        {
            string serialized = sr.ReadToEnd();
            return serialized;
        }
    }            
}

static public T DeserializeFromString<T>(string serializedDataAsString)
{
    DataContractSerializer s = new DataContractSerializer(typeof(T));
    using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(serializedDataAsString)))
    {
        object s2 = s.ReadObject(ms);
        return (T)s2;
    }
}

Answer 1

在反序列化时,既不调用构造函数也不调用字段初始值设定项,而是使用"空白"未初始化对象.

要解决它,您可以使用OnDeserializing或OnDerserialized属性让反序列化器调用具有以下签名的函数:

void OnDeserializing(System.Runtime.Serialization.StreamingContext c);

在该函数中,您可以初始化反序列化过程中遗漏的任何内容.

在约定方面,我倾向于让我的构造函数调用一个方法OnCreated(),然后还有deserializating方法调用相同的东西.然后,您可以在那里处理所有字段初始化,并确保在反序列化之前触发它.

[DataContract]
public abstract class MyAbstract
{
    protected Dictionary<int, string> myDict;

    protected MyAbstract()
    {
        OnCreated();
    }

    private void OnCreated()
    {
        myDict = new Dictionary<int, string>();
    }

    [OnDeserializing]
    private void OnDeserializing(StreamingContext c)
    {
        OnCreated();
    }

    private bool MyMethod(int key)
    {
        return myDict.ContainsKey(key);
    }

    private int myProp;

    [DataMember]
    public int MyProp
    {
        get { return myProp; }
        set { bool b = MyMethod(value); myProp = value; }
    }
}

Answer 2

另一种方法是通过受保护的(在您的示例中)属性访问您的字段,并使用null-coalescing(??)运算符初始化该字段

protected Dictionary<int, string> myDict = new Dictionary<int, string>(); 

protected Dictionary<int, string> MyDict
{
    get
    {
        return myDict ?? (myDict = new Dictionary<int, string>());
    }
}

缺点是您失去了好处readonly,并且需要确保您只通过该属性访问该值.